Characterization of metal complexes in Kuwait atmospheric residues

Four kinds of atmospheric residues (ARs) from Kuwait crudes were characterized using various analytical tools. V- and Ni petroporphyrins present in the four ARs could be analyzed by gas chromatography-atomic emission detection with high-temperature injection. All the ARs exhibited definite peaks for the vanadium and nickel species. Chromatograms of vanadium and nickel consist of a broad peak superimposed with sharp peaks corresponding to the retention times of porphyrin. Demetallation of ARs on the silica-alumina (support only) catalyst alone decreased the intensity of the sharp peaks preferentially over the broad one. ARs exhibited electron spin resonance (ESR) with the species V=O, whose line profiles were different from that of V=O tetraphenylporphyrin in tetrahydrofuran at room temperature. The profiles, however, resemble those of the frozen form (- 150 °C), indicating limited mobility of petroporphyrin in the AR at room temperature. The limited mobility, revealed by ESR, and the favorable effects of hydrogenation conditions for hydrodemetallization suggest the covalent and noncovalent binding of some petroporphyrins to the polymeric component in the as-received forms of ARs. Liberation of petroporphyrin from the gas chromatograph column at around 450 °C may occur and generate monomeric forms that reach the detector.